261551566 has 8 divisors (see below), whose sum is σ = 393513624. Its totient is φ = 130380360.

The previous prime is 261551539. The next prime is 261551567. The reversal of 261551566 is 665155162.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261551567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 196885 + ... + 198208.

It is an arithmetic number, because the mean of its divisors is an integer number (49189203).

Almost surely, 2^261551566 is an apocalyptic number.

261551566 is a deficient number, since it is larger than the sum of its proper divisors (131962058).

261551566 is a wasteful number, since it uses less digits than its factorization.

261551566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 395426.

The product of its digits is 54000, while the sum is 37.

The square root of 261551566 is about 16172.5559513640. Note that the first 3 decimals coincide. The cubic root of 261551566 is about 639.5175123268.

It can be divided in two parts, 26155156 and 6, that added together give a palindrome (26155162).

The spelling of 261551566 in words is "two hundred sixty-one million, five hundred fifty-one thousand, five hundred sixty-six".